1. Field of the Invention
The invention relates to a leak test apparatus and a leak test method that tests for a leak in a workpiece by sealing an open portion formed on one side surface of the workpiece.
2. Description of Related Art
A leak test apparatus that tests for a leak in a workpiece such as a cylinder block by sealing an open portion formed on one side surface of the workpiece is used in an engine production line or the like (see Japanese Patent Application Publication No. 2002-328066 (JP 2002-328066 A), for example). The leak test apparatus described in JP 2002-328066 A is provided with a plurality of masking seals and the like on a movable base that is arranged facing one side surface of a workpiece (i.e., an object to be tested). The movable base is connected to driving means such as a cylinder, and the movable base is able to be extended and retracted with respect to the workpiece. The leak test apparatus described in JP 2002-328066 A moves the movable base close to the workpiece with the driving means, and seals all of the plurality of open portions with the masking seals.
The leak test apparatus described in JP 2002-328066 A brings all of the masking seals into contact with the workpiece and compresses them by driving one of the driving means. Therefore, this leak test apparatus is not able to selectively seal only a desired open portion, from among the plurality of open portions. That is, even if the plurality of open portions is to be tested in order, the driving means must compress the masking seals by generating a large enough amount of thrust to be able to seal the plurality of open portions simultaneously.
Here, as the structure of the masking seals described in JP 2002-328066 A, for example, a fixed rubber member 620 that is fixedly attached to a movable base 610, and a movable rubber member 631 that is attached to the movable base 610 via a spring 630, and the like, as shown in FIG. 14A, are conceivable. In this case, a cylinder 640 brings the fixed rubber member 620 and the movable rubber member 631 (via the spring 630) into contact with the workpiece and compresses them, by generating thrust toward the left (i.e., leftward thrust). Thus, with the thrust generated on the masking seals, the cylinder 640 seals a first open portion W11 formed on an upper side of a workpiece W10, and a second open portion W12 that is arranged in a position below the first open portion W11 and offset by a predetermined length to the left from the first open portion W11.
Hereinafter, the thrust required to seal the first open portion W11 will be designated F11, and the thrust required to seal the second open portion W12 will be designated F12. Also, these thrusts F11 and F12 include reaction force generated during the test.
If the second open portion W12 is farther away from the first open portion W11 side by a tolerance (hereinafter also referred to as “distance”) d more than a normal dimension (i.e., the dimension of the second open portion W12 shown in FIG. 14A), the rubber members 620 and 631 will abut against the open portions W11 and W12 at the same time, as shown in FIG. 14B. In this case, the cylinder 640 generates the thrusts F11 and F12 on the masking seals by generating a leftward thrust N61 that is equal to the sum of the thrusts F11+F12, thereby sealing the open portions W11 and W12 (see rightward reaction forces H11 and H12 in FIG. 14B).
On the other hand, if the second open portion W12 is closer to the first open portion W11 side by the distance d more than the normal dimension (i.e., the dimension of the second open portion W12 shown in FIG. 14A), the movable rubber member 631 will abut against the second open portion W12 before the fixed rubber member 620 abuts against the first open portion W11, as shown in FIG. 14C. Therefore, in order to seal the first open portion W11, the spring 630 must be pressed all the way by the leftward thrust of the cylinder 640. When the spring constant of the spring 630 is k, the cylinder 640 must also generate a thrust 2kd to absorb the distance d, in addition to the leftward thrust that is equal to the sum of the thrusts F11+F12 (see thrust N62 in FIG. 14C).
Also, one conceivable structure for sealing the open portions W11 and W12 seals both of the open portions W11 and W12 by fixed rubber members 620 and 650, as shown in FIG. 15A, for example. In this case as well, when the second open portion W12 is closer to the first open portion W11 side by a distance d more than the normal dimension (i.e., the dimension of the second open portion W12 shown in FIG. 15A), the cylinder 640 must generate a thrust G to absorb the distance d (see thrust N64 in FIG. 15C).
Here, as shown in FIG. 16, with the thrust generated by compressing the fixed rubber member 650, the compression amount increases linearly from 0 to a predetermined amount, and then increases nonlinearly beyond this predetermined amount. Also, the rubber members 620 and 650 are compressed, so the compression amount of the fixed rubber member 650 is unable to be determined based on the stroke of the cylinder 640.
That is, with a structure such as that shown in FIG. 15A, the compression amount of the fixed rubber member 650 that is necessary to generated the thrust F12 is unable to be ascertained. In this case, it is necessary to increase the natural length of the fixed rubber member 650 and increase the compression amount to ensure the thrust F12 (extra allowance (i.e., extra length) must be provided). That is, the cylinder 640 must further generate a thrust ΔF to overcome the extra allowance (i.e., the extra length of the fixed rubber member 650) (see thrusts N63 and N64 in FIGS. 15B and 15C).
As described above, the leak test apparatus described in JP 2002-328066 A requires driving means having more thrust than the thrust for sealing the open portion.